Surface contour imaging uses patterned or structured light and triangulation to obtain surface contour information for an object. In contour imaging, a pattern of lines or other features is projected toward the surface of an object from a given angle. The projected pattern on the surface is then viewed from another angle as a contour image, taking advantage of triangulation in order to analyze surface information and to characterize the surface contour based on the deformed appearance of the projected lines. Phase shifting, in which the projected line pattern is incrementally spatially shifted for obtaining additional measurements at higher resolution, helps to more accurately map the object's surface.
Surface contour imaging using structured light has been employed in a number of applications for determining the shape of solid, highly opaque objects. Contour imaging has also been used for characterizing the surface shape of portions of the anatomy and for obtaining detailed data about skin structure. However, a number of technical obstacles complicate effective use of contour projection imaging of the tooth. Among recognized problems for surface contour imaging of teeth are tooth translucency, high reflection levels, and the complex structure of the teeth itself.
There have been a number of attempts to adapt structured light surface-profiling techniques to the problems of tooth structure imaging. For example, U.S. Pat. No. 5,372,502 entitled “Optical Probe and Method for the Three-Dimensional Surveying of Teeth” to Massen et al. describes the use of an LCD matrix to form patterns of stripes for projection onto the tooth surface. A similar approach is described in U.S. Patent Application Publication 2007/0086762 entitled “Front End for 3-D Imaging Camera” by O'Keefe et al. U.S. Pat. No. 7,312,924 entitled “Polarizing Multiplexer and Methods for Intra-Oral Scanning” to Trissel describes a method for profiling the tooth surface using triangularization and polarized light, but requiring application of a fluorescent coating for operation. Similarly, U.S. Pat. No. 6,885,464 entitled “3-D Camera for Recording Surface Structures, in Particular for Dental Purposes” to Pfeiffer et al. discloses a dental imaging apparatus using triangularization but also requiring the application of an opaque powder to the tooth surface for imaging. U.S. Pat. No. 6,885,464 to Pfeiffer et al. describes an intraoral camera that provides a group of light beams for imaging. Patent Application WO 2011/145799 by Lim describes a 3-D scanner using scanned laser light.
At least one problem that presents an inherent difficulty for surface contour imaging of the teeth relates to the challenge of scanning surfaces within the confined space of the patient's mouth. It can be difficult to position the intraoral camera in a comfortable and stable position for imaging, to retain the scanner in place and/or to reduce or minimize operator or patient movement or fixture vibration while the contour images are being acquired. As a result of unintentional movement during scanning, various types of image artifacts can be generated, compromising the overall accuracy of surface reconstruction, affecting the appearance, and/or affecting the smoothness of the final mesh surface that is typically generated.
Thus, it can be appreciated that there would be benefits to an optical apparatus and method for intraoral surface contour imaging that detects and reports image artifacts resulting from relative movement between the intraoral camera and the subject teeth and other features.